Fluorescent pseudomonads are commonly found in plant rhizosphere soil. Certain strains of these bacteria have been demonstrated to promote plant growth by suppressing plant pathogens. Mechanisms of these strains involve the production of siderophores, hydrogen cyanide (HCN) and antibiotics (Douglas and Gutterson, Applied and Environmental Microbiology 52:1183-1189 (1986)). Several disease-suppressive antibiotics, N-containing heterocyclics such as phenazine 1-carboxylic acid (PCA) (Gerber, Journal of Heterocyclic Chemistry 6:297-300 (1969); Thamashow et al. Applied and Environmental Microbiology 56:908-912 (1990); Slininger and Willbur, Applied and Environmental Microbiology 43:794-800 (1995)), phenazine-1-carboxamide (PCN) (Chin-A-Woeng et. al. Molecular Plant-Microbe Interaction 11:1069-1077 (1998)), acetamidophenol (Slininger et al. Applied Microbiology and Biotechnology 54:376-381 (2000)), pyrrol-type antibiotics (Hashimoto and Hattori, Bulletin of Chemical Society of Japan 39:410 (1966a) and Hashimoto and Hattori, Chemical and Pharmaceutical Bulletin 14:1314-1316 (1966b)), pyo-compounds (Hays et al. Journal of Biological Chemistry 159:725-750 (1945)), indoles (Wratten et al. Antimicrobial Agents and Chemotherapy 11:411-414 (1977)) and diacetylphloroglucinol (Shanahan et al. Applied and Environmental Microbiology 58:353-358 (1992) produced by fluorescent pseudomonads have been reported. The core biosynthetic pathway of phenazine is highly conserved in fluorescent Pseudomonas spp. ((Delaney et al. Journal of Bacteriology 183(1):318-327 (2001)). Species of fluorescent pseudomonads such as P. fluorescens (Thamashow et al. Applied and Environmental Microbiology 56:908-912 (1990)), P. aureofaciens (Toohey et al. Canadian Journal of Botany 43:1055-1062 (1965)) and P. aeruginosa (Fernandez and Pizaro, Journal of Chemotherapy A 771:99-104 (1997)) have been reported for the production of more than one phenazine. Although different phenazines have been found with the same structure, they differ in the derivatization of the heterocyclic core. These modifications of heterocyclic core largely determine the physical properties of phenazines and influence their antimicrobial activity against pathogens. However, the broad-spectrum activity of phenazines against fungi and bacteria is not understood so far. The biochemistry and genetics of phenazine synthesis has not been understood completely (Delaney et al. Journal of Bacteriology 183(1): 318-327 (2001)). Transgenic fluorescent Pseudomonas spp. that produce PCA as well as 2,4-diacetylphloroglucinol have been used as biocontrol agents against soil-borne fungal pathogens (Pythium, Gaeumannomyces graminis and Rhizoctonia) of food, fiber and oramental plants (Huang et al. U.S. Pat. No. 6,277,625 (2001). The PCA from P. fluorescens 2-79 has been characterized by Gurusiddaiah et al. (Antimicrobial Agents and Chemotherapy 29:488-495 (1986)) and the gene cluster involved in the biosynthesis has also been reported (McDonald et al. Journal of American Chemical Society 123: 9459-9460 (2001). Brisbane et al. (Antimicrobial Agents and Chemotherapy 31:1967-1971 (1987)) made criticism on the usefulness of PCA or PCA producing bacteria as effective biocontrol agents against phytopathogens in alkaline environments due to their pH dependency. In vitro tests clearly indicated that the PCA from P. fluorescens 2-79 is ineffective in alkaline pH due to complete ionization to an inactive carboxylate ion (Brisbane et al. Antimicrobial Agents and Chemotherapy 31: 1967-1971 (1987)).